The present invention relates generally to a construction method and more particularly to a method for constructing an elongated concrete structure, particularly a multiple-span bridge superstructure made of reinforced or prestressed concrete. The invention is especially concerned with a construction technique wherein a formwork device arranged in the immediate vicinity of one end of the site across which the structure is to extend is utilized to form the structure in discrete successive sections, with each section being connected to a previously formed section by means of untensioned or prestressed connecting reinforcement elements which are moved together with the sections progressively and in series toward the opposite side of the site of the structure.
A prior art method of the type herein discussed is known under the designation "incremental launching method" (see German Pat. No. 1,237,603). In this method, the bottom slab of a hollow box is first constructed on a lowerable bottom formwork at the location where the sections of the structure are constructed. The bottom formwork is displaced relative to the actual stationary formwork from the hollow box by the length of a section of the structure. The bottom formwork is lowered after the concrete of the bottom slab has hardened. During this procedure, the slab is placed on prepared slide bearings upon which the slab is moved. Subsequently, upper portions of the respective sections of the structure are constructed in the region of the stationary formwork which also includes an internal formwork. The internal formwork is moved back after the respective sections of the structure have been moved forwardly.
Each completed section of the structure is moved by a device which consists of a combination of vertically and horizontally acting hydraulic press means. By operation of the vertically acting press means, a slight lifting of the superstructure produces a friction grip between the press and the superstructure as a result of which the horizontally acting press means may then effect a desired forward movement. In order to enable lowering of the formwork for the bottom slab, it is necessary to provide a sufficient space beneath the formwork. This leads to the formation of a so-called "cellar" beneath the construction site.
In the incremental launching method many simplifications in the construction of elongated structures are facilitated. For example, the formwork mechanism may be reused repeatedly. On the other hand, the method is rather expensive and it can, therefore, only be used advantageously in the construction of long and heavy bridges.
The present invention is directed to providing means whereby procedures such as the incremental launching method may be simplified particularly with respect to the material and time requirements involved in bridge construction. The invention thus is directed toward making such methods useful for smaller bridges.